1. Field of the Invention
The invention generally relates to methods, systems and devices for detecting solid particles in a flowing fluid within a medium.
2. Background of the Invention
Methods and equipment for detecting solid particles in a flowing fluid is known already, where solid particles such as sand grains are often entrained in a flowing fluid that is recovered from an underground formation. For example, sand can cause damage to pipes, pumps, valves, fluid treating installations on the surface, and other related oil production or exploration equipment. Also the production of sand may result in clogged well lines that can result in filling in the well and stopping production. When this clogging occurs, the production of all oil wells feeding into the separator tanks must be stopped. Generally, the presence of sand can be dependent upon how an oil related fluid (such as gas and/or liquid hydrocarbons) was produced and the nature of the production reservoir. It is possible that a significant amount of sand can be present when an oil related fluid is produced from a reservoir. Also, sand can also be present with hydrocarbon fluids when produced in gravel pack operations which are experiencing partial or complete failure. In order to prevent such a costly expense, an early warning system is required to detect the presence of those amounts of sand grains that can be expected to cause damage of the recovery equipment in the well or on the production site.
A known method for detecting individual solid particles carried in a particular flow area of a flowing fluid includes grains impinging on a piezoelectric transducer. The peak value of the resulting electric output signal is detected in a pulse height discriminator after a suitable amplification of this signal. When the peak value exceeds a pre-set discrimination level, a standard output pulse is produced with a length that is greater than the typical duration of the impact signal. The number of standard pulses is counted in a pre-determined period. At a given velocity, the grain diameter can be estimated from the peak amplitude of the impact response, and a differentiation can be made between different ranges of grain sizes which will lead to a grain-size distribution of the grains that pass through a given area of the cross-section of the conduit over a given period (see Background section of U.S. Pat. No. 4,240,287).
Another method for detecting solid particles, such as sand, moving in a flowing fluid includes a sensor that generates signals in response to particle impact (see U.S. Pat. No. 4,240,287). Such a sensor conventionally comprises a piezo-electric element coupled to the sensor housing so that collision of particles with the housing deform the element, causing the latter to generate a voltage signal which may be analyzed to obtain information on the nature of the impact. For example, the signal can be amplified, unwanted frequency components filtered-out and a thresh-holding procedure is then applied in order to determine whether the amplitude of the signal is greater than a pre-determined threshold level. If that threshold is passed, the detection of an impact is registered in a counter.
Because the magnitude of the sensor signal is related to the force of particle impact, a series of different threshold levels may be employed in order to give an indication of the relative magnitudes of particle impacts. The energy dissipated on impact is proportional to the momentum of the particle involved, from which an indication of the mass of the particle can be obtained if the velocity of impact is known (or deduced from, for example, the flow-rate of the fluid). An example of such an arrangement is shown in U.S. Pat. No. 4,240,287. However, one disadvantage of such an arrangement is that an accurate measure of particle size is not obtained, since the various impact signals are merely sorted into a number of ranges dictated by the threshold levels.
Other sand detector methods may include fiber optic sensors and flowmeters which provide for monitor parameters such as fluid sound speed, fluid velocity, pressure, and temperature. Such fiber optic based flowmeters are disclosed in the following U.S. Patents, and are hereby incorporated by reference in their entireties: U.S. Pat. No. 6,782,150, entitled “Apparatus for Sensing Fluid in a Pipe;” U.S. Pat. No. 6,691,584, entitled “Flow Rate Measurements Using Unsteady Pressures;” and U.S. Pat. No. 6,354,147, entitled “Fluid Parameter Measurement in Pipes Using Acoustic Pressures,” hereinafter referred to as the “flowmeter references.” However, these flowmeter references fail to provide any ability to reliably monitor sand production at the surface or downhole in real-time. At least one disadvantage over the above-note prior art is that sonic techniques generally detect the presence of sand particles, but not other attributes, e.g., grain sizes, velocities, etc., all of which, among other things, are important to assess the potential erosion, for example to oil field applications such as pipes and/or equipment. Further, sonic techniques are also not sensitive, if at all, when the sand population is low.
Therefore, there exists a need for methods, systems and/or devices for detecting solid particles in a flowing fluid using sources such as x-rays or some other source, for example, detecting sand particles in a flowing fluid so as to provide sand analysis information.